Structural highlights
Function
[POLN_EEVVP] P123 and P123' are short-lived polyproteins, accumulating during early stage of infection. P123 is directly translated from the genome, whereas P123' is a product of the cleavage of P1234. They localize the viral replication complex to the cytoplasmic surface of modified endosomes and lysosomes. By interacting with nsP4, they start viral genome replication into antigenome. After these early events, P123 and P123' are cleaved sequentially into nsP1, nsP2 and nsP3/nsP3'. This sequence of delayed processing would allow correct assembly and membrane association of the RNA polymerase complex (By similarity). nsP1 is a cytoplasmic capping enzyme. This function is necessary since all viral RNAs are synthesized in the cytoplasm, and host capping enzymes are restricted to the nucleus. The enzymatic reaction involves a covalent link between 7-methyl-GMP and nsP1, whereas eukaryotic capping enzymes form a covalent complex only with GMP. nsP1 capping would consist in the following reactions: GTP is first methylated and then forms the m7GMp-nsP1 complex, from which 7-methyl-GMP complex is transferred to the mRNA to create the cap structure. Palmitoylated nsP1 is remodeling host cell cytoskeleton, and induces filopodium-like structure formation at the surface of the host cell (By similarity). nsP2 has two separate domain with different biological activities. The N-terminal section is part of the RNA polymerase complex and has RNA trisphosphatase and RNA helicase activity. The C-terminal section harbors a protease that specifically cleaves and releases the four mature proteins. Also inhibits cellular transcription by inducing rapid degradation of POLR2A, a catalytic subunit of the RNAPII complex. The resulting inhibition of cellular protein synthesis serves to ensure maximal viral gene expression and to evade host immune response (By similarity). nsP3 and nsP3' are essential for minus strand and subgenomic 26S mRNA synthesis. nsP4 is an RNA dependent RNA polymerase. It replicates genomic and antigenomic RNA by recognizing replications specific signals. Transcribes also a 26S subgenomic mRNA by initiating RNA synthesis internally on antigenomic RNA. This 26S mRNA codes for structural proteins. nsP4 is a short-lived protein regulated by several ways: the opal codon readthrough and degradation by ubiquitin pathway (By similarity).
Evolutionary Conservation
Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf.
Publication Abstract from PubMed
Macro domains (also called "X domains") constitute a protein module family present in all kingdoms of life, including viruses of the Coronaviridae and Togaviridae families. Crystal structures of the macro domain from the Chikungunya virus (an "Old World" alphavirus) and the Venezuelan equine encephalitis virus (a "New World" alphavirus) were determined at resolutions of 1.65 and 2.30 A, respectively. These domains are active as adenosine di-phosphoribose 1-phosphate phosphatases. Both the Chikungunya and the Venezuelan equine encephalitis virus macro domains are ADP-ribose binding modules, as revealed by structural and functional analysis. A single aspartic acid conserved through all macro domains is responsible for the specific binding of the adenine base. Sequence-unspecific binding to long, negatively charged polymers such as poly(ADP-ribose), DNA, and RNA is observed and attributed to positively charged patches outside of the active site pocket, as judged by mutagenesis and binding studies. The crystal structure of the Chikungunya virus macro domain with an RNA trimer shows a binding mode utilizing the same adenine-binding pocket as ADP-ribose, but avoiding the ADP-ribose 1-phosphate phosphatase active site. This leaves the AMP binding site as the sole common feature in all macro domains.
The crystal structures of Chikungunya and Venezuelan equine encephalitis virus nsP3 macro domains define a conserved adenosine binding pocket.,Malet H, Coutard B, Jamal S, Dutartre H, Papageorgiou N, Neuvonen M, Ahola T, Forrester N, Gould EA, Lafitte D, Ferron F, Lescar J, Gorbalenya AE, de Lamballerie X, Canard B J Virol. 2009 Jul;83(13):6534-45. Epub 2009 Apr 22. PMID:19386706[1]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
References
- ↑ Malet H, Coutard B, Jamal S, Dutartre H, Papageorgiou N, Neuvonen M, Ahola T, Forrester N, Gould EA, Lafitte D, Ferron F, Lescar J, Gorbalenya AE, de Lamballerie X, Canard B. The crystal structures of Chikungunya and Venezuelan equine encephalitis virus nsP3 macro domains define a conserved adenosine binding pocket. J Virol. 2009 Jul;83(13):6534-45. Epub 2009 Apr 22. PMID:19386706 doi:10.1128/JVI.00189-09
